The present invention relates to an improved breechblock assembly and an operating mechanism thereof for a gas operated automatic loading fire-arm.
Heretofore, a breechblock assembly incorporated in an automatic loading fire-arm of this type has been constituted by a breechblock effective to tightly close the breech face of the barrel of a gun, a backward movement regulating locking block of the aforementioned breechblock which disengageably engages the barrel and which tightly closes the said breech face when engaged with the barrel, and a breechblock slider attached to the breechblock so as to be movable forwardly and backwardly within a predetermined distance and moved backwardly when the gas pressure generated by the firing of a shotshell is transmitted thereto through a gas operated means so as to move the breechblock integrally therewith after releasing of the backward movement of the breechblock locked by the locking block as the breechblock moves in its backward stroke.
In other words, the general construction of the above described breechblock assembly is so constructed that, as shown in FIGS. 1 and 2, the breechblock slider (30) is mounted on the lower portion of the breechblock (29) so as to be forwardly and backwardly movable for a predetermined distance, and a radially directed throughhole (31) is formed at the central portion of the breechblock (29) so as to house therein the locking block (32) so that the projection (33) formed on the locking block (32) for engaging with the barrel of the gun (not shown) is swung upward and downward in response to the relative movement of the breechblock slider (30) with respect to the breechblock (29).
However, with such a construction as described above, the following problems listed below will act as hindrances. That is to say, in order to closely lock the breechblock (29) to the breech face of the barrel in relation to the projection (33) of the locking block to the barrel extension of the barrel, and since the operational force of the gas pressure generated by firing of the shotshell against the face of the breechblock (29) is regulated by the barrel through the aforementioned locking block (32), the forces F.sub.1, F.sub.2 indicated by the arrows in the drawing are given to the locking block (32) so as to generate a rotational movement due to the construction of the locking block (32), and the locking block (32) undergoes a clockwise rotation about the point A in the drawing resulting in collision of the rear end portion of the breechblock (32) opposite to the projection (33) against the inner wall of the barrel or the receiver, and, at the same time, the area of the collision of the locking block (32) against the front wall surface of the throughhole (31) of the breechblock (29) is located adjacent to the point A which is the above described center of rotation and becomes substantially linear so that the area of the pressure receiving surface of the above described force is small thereby requiring high rigidity and high strength of the breechblock (29) and the locking block (32).
Further, after releasing the locking of the locking block (32), the locking block (32) is made free in the throughhole (31) of the breechblock (29), so that it might leap freely during the forward and backward stroke of the breechblock assembly, therefore, it is conventional to provide necessary guide rails on the inner wall of the receiver to prevent malfunction of the locking block (32) caused by entanglement with the inner wall of the receiver or the like.
In case the rear end portion of the locking block (32) opposite to the side at which the projection (33) is provided is shifted to the breechblock (29), the pivot shaft portion is subjected to the above described rotational movement, therefore, it is necessary to increase the strength of that portion subjected to the rotational movement and to enhance the accuracy of the relative dimensions between the pivot shaft and the front wall surface of the throughhole (31) of the breechblock (29) as well as the locking block (32), thereby causing undesirable troubles in constructing the breechblock assembly.
The operating mechanism of the breechblock assembly (this terminology refers hereinafter to the breechblock, the breechblock slider and the locking block, etc. as a whole) is so constructed that the load due to the gas pressure at the firing of a shotshell is transmitted to the breechblock assembly in the receiver through a gas operated means mounted on the side of the barrel so that the breechblock assembly locked in a tightly closed relationship to the breech face is caused to recoil after a certain delayed timing of the action so as to discharge a used empty cartridge and then the breechblock assembly is forced to move forwardly by the force of the recoil spring housed in the gun-stock so as to be ready for charging a new shotshell and shooting of the same.
In a conventional construction of the breechblock assembly, a link is interposed between the above described breechblock assembly and the recoil spring which is pivoted to the breechblock slider of the breechblock assembly for the upward and downward swinging movement thereof. Since such a mechanism is so constructed that the breechblock assembly is provided with a breechblock adapted to be locked in a tightly closed manner to the breech face and a breechblock slider movable forwardly and backwardly within a predetermined distance with respect to the breechblock and coupled with the above described gas operated means, so that the breechblock slider is first moved backward at the firing of a shotshell so as to release the locking between the breechblock and the breech face thereby backwardly moving the breechblock integrally as a whole. Therefore, it is necessary to connect a link between the breechblock slider and the recoil spring in order to restore the breechblock assembly to its initial position by the resilient force of the recoil spring, and the configuration of the gun stock is in such a form that the shooter uses his shotgun with the breech thereof against his shoulder. Therefore, the link which is inclined to a certain degree with respect to the forward and backward movement of the breechblock assembly as is well known and is guided by the recoil spring housed in the gun stock must be made temporarily tiltable with respect to the breechblock assembly.
As described above, it is important that the breechblock assembly and, particularly, the breechblock are held in a locked state during the predetermined delay in the timing of the operation wherein the breech face is tightly closed. And it is the usual manner that the breechblock assembly is caused to be moved backward as a whole after the above described locking is released by the backward movement of the breechblock slider. However, if the locking state of the breechblock is not appropriate, it is not unusual that malfunctions as such that the breechblock immediately moves backward, simultaneously with the firing of a shotshell, are caused. In such a case, since the shotshell is discharged from the barrel by the backward movement of the breechblock, the shotshell is sprung out of the barrel under the condition that the proper combustion of the gunpowder is being commenced, thereby resulting in a serious danger wherein the shooter is exposed to the ejection of the burning gas of the powder and injured.